Light emitting structure to aid LED light extraction

ABSTRACT

Display panels and methods of manufacture are described for down converting a peak emission wavelength of a pump LED within a subpixel with a quantum dot layer. In some embodiments, pump LEDs with a peak emission wavelength below 500 nm, such as between 340 nm and 420 nm are used. QD layers in accordance with embodiments can be integrated into a variety of display panel structures including a wavelength conversion cover arrangement, QD patch arrangement, or QD layers patterned on the display substrate.

RELATED APPLICATIONS

This patent application is a continuation of co-pending U.S. patentapplication Ser. No. 16/375,614, filed Apr. 4, 2019, which is acontinuation of U.S. patent application Ser. No. 15/740,739 filed Dec.28, 2017, now U.S. Pat. No. 10,297,581, which is a U.S. National PhaseApplication under 35 U.S.C. § 371 of International Application No.PCT/US2016/041005, filed Jul. 5, 2016, which claims the benefit ofpriority of U.S. Provisional Application No. 62/189,601 filed Jul. 7,2015, of which PCT Application No. PCT/US2016/041005 and U.S.Provisional Application No. 62/189,601 are incorporated herein byreference in their entirety.

BACKGROUND Field

Embodiments described herein relate to a display system, and morespecifically to the integration of quantum dots into the display area ofa display panel.

Background Information

Light emitting diodes (LED) are now commonly found in a variety oflighting systems. LED lighting can be more efficient, durable,versatile, and longer lasting than conventional incandescent andfluorescent lighting systems. For example, LEDs can be designed from avariety of organic and inorganic semiconductor materials to achievespecific emission colors. In order to achieve a white light, differentcolor LEDs can be mixed or covered with a phosphor material to convertthe color of light.

One type of commonly employed phosphor material is a particle thatexhibits luminescence due to its composition, such as a cerium dopedyttrium aluminum garnet (YAG:Ce). Another phosphor material is a quantumdot. Quantum dots are semiconductor materials where the size of thestructure is small enough that the electrical and opticalcharacteristics differ from the bulk properties due to quantumconfinement effects. Due to the small size, such as 1 to 100 nm, or moretypically 1 to 20 nm, quantum dots display unique optical propertiesthat are different from those of the corresponding bulk material, andcan be tuned to emit light throughout the visible and infrared spectrum.The wavelength, and hence color, of the photo emission is stronglydependent on the size of a quantum dot. For an exemplary cadmiumselenide (CdSe) quantum dot, light emission can be gradually tuned fromred for a 5 nm diameter quantum dot, to the violet region for a 1.5 nmquantum dot. One proposed implementation for quantum dots is integrationinto the backlighting of a liquid crystal display (LCD) panel.

SUMMARY

Display systems and display panels with integrated quantum dot layersare described. In an embodiment, a display panel includes a plurality ofLEDs mounted on a display substrate and arranged in a pixel of a pixelarray. A first LED is arranged in a first subpixel designed to emit afirst peak emission wavelength (e.g. in the red spectrum). A second LEDis arranged in a second subpixel designed to emit a second peak emissionwavelength (e.g. in the green spectrum). A third LED is arranged in athird subpixel designed to emit a third peak emission wavelength (e.g.in the blue spectrum). Thus, the first, second, and third peak emissionwavelengths may be different.

A quantum dot (QD) layer can be aligned over any of the LEDs to emit anyof the first, second, or third peak emission wavelengths. Sucharrangements may allow for the integration of QD layers over efficientpump LEDs in which a pump LED peak emission wavelength is converted bythe QD layer to the subpixel emission wavelength.

In an embodiment, a QD layer is aligned over the first LED, and the QDlayer includes QDs designed to emit the first peak emission wavelength.In accordance with embodiments, the first LED (e.g. pump LED) has a peakemission wavelength that is shorter than the first absorption peak inthe QD absorption spectrum (e.g. band edge). For example, this may beany wavelength below 500 nm. In an embodiment, the first LED has a peakemission wavelength between 380 nm and 420 nm, and the QD layer includesQDs designed to emit the first peak emission wavelength (e.g. in the redspectrum). In an embodiment, the QD layer is aligned over both the firstLED and the second LED, and the second peak emission wavelength iswithin a green color spectrum.

The QD layers may include QDs arranged in a variety of form factorsincluding dispersed or embedded in matrix materials (e.g. glass,sol-gel, polymer, cross-linked materials), as particles in neat films,within beads, etc. Additionally, various volume loadings (packingdensity) can be achieved, such as greater than 20% by volume, or morespecifically greater than 40% by volume. In some embodiments, QD layerthicknesses of 1-100 μm and packing densities of 1-60% may be utilized.Thus, the QDs can be more widely dispersed, or formed in close packedfilms with high volume density. In some embodiments, thickness of the QDlayers can be reduced to less than 20 μm, or even less than 5 μm bycontrolling various parameters such as pump LED peak emissionwavelength, QD volume loading, QD emission re-absorption, pump LEDfilters, scattering agents, mirror layers, etc. A reduced QD layerthickness may facilitate incorporation into high resolution displays,e.g. with high pixels per inch (PPI). In an embodiment, QDs within theQD layer are embedded in a cross-linked matrix of ligands bound to theQDs.

A variety of different layers may optionally be located above or belowthe QD layer, for example, to decrease bleeding of pump LED light, orincrease efficiency of the QD layer. In some embodiments, a Braggreflector layer may be located between the first LED and the QD layer.In such a configuration, the Bragg reflector layer is transparent to thepeak emission wavelength of the first LED and reflective to the firstpeak emission wavelength of the QDs. In some embodiments, a Braggreflector layers is located over the QD layer. In such a configuration,the Bragg reflector layer is transparent to the first peak emissionwavelength of the QDs and reflective of the peak emission wavelength ofthe first LED. In some embodiments, a color filter layer is located overthe QD layer to absorb the peak emission wavelength of the first LED.

QD layers in accordance with embodiments can be integrated into avariety of display panel structures including a wavelength conversioncover arrangement, QD patch arrangement, or QD layers patterned on thedisplay substrate.

In an embodiment, the display panel includes a wavelength conversioncover over the first LED, the second LED, and the third LED mounted onthe display substrate, where the wavelength conversion cover includesthe QD layer embedded in a cover film. The wavelength conversion covermay additionally include a second QD layer embedded in the cover filmand aligned over the second LED, with the second QD layer including QDsdesigned to emit at the second peak emission wavelength (e.g. the greenspectrum). In an embodiment, the wavelength conversion cover does notinclude a QD layer aligned over the third LED (e.g. with a peak emissionwavelength in the blue spectrum). Although, the wavelength conversioncover may include QD layers aligned over all three of the LEDs withinthe pixel.

In an embodiment, the QD layer is within a QD patch, which includes aplanar to surface. The QD patch may include several layers. For example,the QD patch may include a color filter layer over the QD layer toabsorb the peak emission wavelength of the first LED. The QD patch mayinclude a Bragg reflector layer under the QD layer. The Bragg reflectorlayer may be transparent to the peak emission wavelength of the firstLED and reflective of the first peak emission wavelength of the QDs inthe QD layer. In an embodiment, the QD patch includes a Bragg reflectorlayer over the QD layer, and the Bragg reflector layer is transparent tothe first peak emission wavelength of the QDs in the QD layer andreflective of the peak emission wavelength of the first LED. In anembodiment, a second QD patch is aligned over the second LED, with thesecond QD patch including a planar top surface and second QDs design toemit the second peak emission wavelength (e.g. the green spectrum). Inan embodiment, a QD patch is not aligned over the third LED (e.g. with apeak emission wavelength in the blue spectrum). Although, QD patches maybe aligned over all three of the LEDs within the pixel.

In an embodiment, a planarization layer is formed over the displaysubstrate, the planarization layer includes an opening aligned over thefirst LED, and the QD layer is within the opening aligned over the firstLED. In one implementation, a top surface of the QD layer is level witha top surface of the planarization layer. In an embodiment, a secondopening is in the planarization layer and aligned over the second LED. Asecond QD layer may be within the second opening, with the second QDlayer including second QDs designed to emit the second peak emissionwavelength (e.g. the green spectrum). In an embodiment, a QD layer isnot aligned over the third LED (e.g. with a peak emission wavelength inthe blue spectrum). Although, QD layers may be aligned over all three ofthe LEDs within the pixel. In an embodiment, a Bragg reflector layers islocated over one or more of the QD layers. In such a configuration, theBragg reflector layer is transparent to the peak emission wavelength ofthe QDs (in the one or more QD layers) and reflective of the peakemission wavelength of the first LED.

In an embodiment, a display panel includes a display substrate, an arrayof LEDs mounted on the display substrate in an array of pixels, and awavelength conversion cover over the array of pixels. The wavelengthconversion cover includes an array of QD layers embedded in a coverfilm, with the array of QD layers aligned over the array of LEDs. Thecover film may include an array of cavities formed in a bottom surfaceof the cover film, with the array of QD layers contained (e.g. embedded)within the array of cavities. A color filter layer may be formed withinthe array of cavities to absorb a peak emission wavelength of the arrayof LEDs. In an embodiment, the array of LEDs (e.g. pump LEDs) may bedesigned to emit a peak emission wavelength between 380 nm and 420 nm.Although pump LEDs may be design to emit alternative peak emissionwavelengths in accordance with embodiments.

The display panel may further include a second array of LEDs mounted onthe display substrate in the array of pixels, with the second array ofLEDs designed to emit a peak emission wavelength above 438 nm (e.g. inthe red, green, or blue spectrums). In an embodiment, the second arrayof LEDs are emitting LEDs, as opposed to pump LEDs, and a QD layer isnot aligned over the second array of LEDs. In an embodiment, the secondarray of LEDs are pump LEDs and may be designed to emit a peak emissionwavelength between 380 nm and 420 nm. In such an embodiment, a secondarray of QD layers may be contained (e.g. embedded) within a secondarray of cavities formed in the bottom surface of the cover film, withthe second array of QD layers aligned over the second array of LEDs.

The display panel may further include an array of light guides in thecover film over the array of cavities, where the light guides arecharacterized by a different refractive index than a bulk of the coverfilm. A transparent fill material may optionally be included within thearray of cavities and over the array of QD layers within the array ofcavities. In an embodiment, a Bragg reflector layer is formed over thearray of LEDs and under the array of QD layers, where the Braggreflector layer is reflective to a peak emission wavelength of the QDscontained within the array of QD layers. In an embodiment, a Braggreflector layer is formed over the array of QD layers, where the Braggreflector layer is transparent to the peak emission wavelength of theQDs contained within the array of QD layers and reflective of the peakemission wavelength of the array of LEDs.

In embodiment, a method of forming a display panel includes forming anarray of cavities in a cover film, forming an array of QD layers withinthe array of cavities, and transferring the cover film including thearray of QD layers to a display substrate, where the array of QD layersare aligned over an array of LEDs mounted on the display substrate. Inan embodiment, the method includes laser fusing cover film regions overthe array of cavities to alter a refractive index of the cover filmregions.

In an embodiment, a display panel includes a display substrate, an arrayof LEDs mounted on the display substrate in an array of pixels, and anarray of QD patches aligned over the array of LEDs, where each QD patchin the array of QD patches includes a planar top surface. The QD patchesmay include multiple layers, such as a QD layer, an optional colorfilter layer over the QD layer, and an optional Bragg reflector layerunderneath the QD layer. In some embodiments, the array of LEDs is anarray of pump LEDs designed to emit a peak emission wavelength between380 nm and 420 nm. A second array of LEDs may be mounted on the displaysubstrate within the array of pixels. The second array of LEDs may beemissive LEDs and may be designed to emit a peak emission wavelengthabove 438 nm. In such a configuration, an array of QD patches is notaligned over the second array of LEDs. In an embodiment, a second arrayof QD patches is aligned over the second array of LEDs. For example, thesecond array of QD patches may be designed to emit a different primarywavelength than the first array of QD patches. In an embodiment thesecond array of LEDs are pump LEDs designed to emit a peak emissionwavelength between 380 nm and 420 nm.

In an embodiment, a method of forming a display panel includeselectrostatically transferring an array of LEDs from an LED carriersubstrate to a display substrate, and electrostatically transferring anarray of QD patches from a QD patch carrier substrate to the displaysubstrate, and aligning the array of QD patches over the array of LEDs.Each QD patch may have a planar top surface, for example, to facilitatecontact with an array of electrostatic transfer heads. Each QD patch mayadditionally include a QD layer and a Bragg reflector layer under the QDlayer. Each QD patch may include a color filter over the QD layer. Themethod may additionally include forming a planarization layer around thearray of QD patches on the display substrate.

In an embodiment, a display panel includes an arrangement of LEDsmounted on a display substrate in an array of pixels. A planarizationlayer is over the array of LEDs, and the planarization layer includes anarray of openings aligned over the array of LEDs. An array of QD layersis within the array of openings aligned over the array of LEDs. A topsurface of each QD layer in the array of QD layers may be level with atop surface of the planarization layer (e.g. they may have beenplanarized). A Bragg reflector layer may be formed over theplanarization layer, where the array of QD layers is over the Braggreflector layer. A top surface of each QD layer in the array of QDlayers may be level with a top surface of the Bragg reflector layer(e.g. they may have been planarized). Alternatively, a Bragg reflectorlayer may be formed over the array of LEDs and underneath theplanarization layer and the array of QD layers. In some embodiments, thearray of LEDs is an array of pump LEDs designed to emit a peakwavelength between 380 nm and 420 nm. In some embodiments, additionalarrays of LEDs are mounted on the display substrate in the array ofpixels. An additional array of LEDs may also be pump LEDs (e.g designedto emit a peak wavelength between 380 nm and 420 nm) or may be emittingLEDs (e.g. designed to emit a peak wavelength above 438 nm) without a QDlayer aligned over the additional array of LEDs. In an embodiment, aBragg reflector layer is formed over the array of QD layers and theplanarization layer, where the Bragg reflector layer is transparent tothe peak emission wavelength of the QDs contained within the array of QDlayers and reflective of the peak emission wavelength of the array ofLEDs.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and not limitation in theFigures of the accompanying drawings.

FIG. 1 is a generalized EQE curve for an inorganic semiconductor-basedLED.

FIG. 2 is a graphical illustration of a CIE 1931 color matchingfunction.

FIG. 3 is an illustration of an RGB display color space overlaying a CIE1976 uniform chromacity diagram (CIE 1976 UCS diagram).

FIG. 4 is a graphical illustration of peak EQE values for InGaN-basedLEDs designed for different color emission in accordance with anembodiment.

FIG. 5 is a schematic illustration of the relationship of QD peakemission, QD absorption, and pump LED peak emission in accordance withan embodiment.

FIG. 6 is an illustration of a process for transferring microdrivers andmicro LEDs from carrier substrates to a display panel in accordance withan embodiment.

FIG. 7 is a schematic top view illustration of a display panel inaccordance with an embodiment.

FIG. 8 is a schematic cross-sectional side view illustration of aportion of a display panel active area in accordance with an embodiment.

FIG. 9 is a schematic cross-sectional side view illustration of a barecore-shell quantum dot with bound ligands in accordance withembodiments.

FIG. 10 is a schematic cross-sectional side view illustration of anano-encapsulated quantum dot in accordance with embodiments.

FIG. 11 is a schematic cross-sectional side view illustration of amicro-encapsulated quantum dot in accordance with embodiments.

FIGS. 12A-12B are schematic cross-sectional side view illustrations fora method of forming a quantum dot layer in accordance with anembodiment.

FIGS. 13A-13B are schematic cross-sectional side view illustrations fora method of forming a quantum dot layer in accordance with anembodiment.

FIGS. 14A-14E are schematic cross-sectional side view illustrations ofLED and quantum dot layer arrangements in a RGB pixel system inaccordance with embodiments.

FIG. 15 a schematic cross-sectional side view illustration of a portionof a display panel including a wavelength conversion cover in accordancewith an embodiment.

FIGS. 16A-16D are schematic cross-sectional side view illustrations ofmethods of forming a wavelength conversion cover in accordance withembodiments.

FIG. 17 is a schematic cross-sectional side view illustration of aportion of a display panel including a wavelength conversion cover inaccordance with an embodiment.

FIGS. 18A-18D are schematic cross-sectional side view illustrations ofmethods of forming a wavelength conversion cover in accordance withembodiments.

FIGS. 19A-19E are schematic cross-sectional side view illustrations ofmethods of forming a display panel including quantum dot patches inaccordance with embodiments.

FIGS. 19F-19G are schematic cross-sectional side view illustrations ofmethods of forming a display panel including layer transfer inaccordance with embodiments.

FIGS. 20A-20E are schematic cross-sectional side view illustrations ofmethods of forming a display panel including quantum dot layers withinopenings in a planarization layer in accordance with embodiments.

FIGS. 20F-20H are schematic cross-sectional side view illustrations ofmethods of forming a display panel including patterning photodefinablequantum dot layers in accordance with embodiments.

FIGS. 21A-21C are schematic cross-sectional side view illustrations ofmethods of forming a display panel including quantum dot layers withinopenings in a planarization layer in accordance with embodiments.

DETAILED DESCRIPTION

In various embodiments, description is made with reference to figures.However, certain embodiments may be practiced without one or more ofthese specific details, or in combination with other known methods andconfigurations. In the following description, numerous specific detailsare set forth, such as specific configurations, dimensions andprocesses, etc., in order to provide a thorough understanding of theembodiments. In other instances, well-known semiconductor processes andmanufacturing techniques have not been described in particular detail inorder to not unnecessarily obscure the embodiments. Reference throughoutthis specification to “one embodiment” means that a particular feature,structure, configuration, or characteristic described in connection withthe embodiment is included in at least one embodiment. Thus, theappearances of the phrase “in one embodiment” in various placesthroughout this specification are not necessarily referring to the sameembodiment. Furthermore, the particular features, structures,configurations, or characteristics may be combined in any suitablemanner in one or more embodiments.

The terms “above”, “over”, “to”, “between”, “spans” and “on” as usedherein may refer to a relative position of one layer with respect toother layers. One layer “above”, “over”, that “spans” or “on” anotherlayer or bonded “to” or in “contact” with another layer may be directlyin contact with the other layer or may have one or more interveninglayers. One layer “between” layers may be directly in contact with thelayers or may have one or more intervening layers.

In accordance with embodiments, a display panel and system is describedincluding an arrangement of inorganic semiconductor-based LEDs andquantum dot layers within the display area of the display panel. In anembodiment, a display panel includes a plurality of LEDs mounted on adisplay substrate and arranged in a pixel in a pixel array. The displaypanel may be a low resolution display or high resolution displaycharacterized by a high pixel per inch (PPI) density. The pixel mayinclude a first subpixel designed to emit a first peak emissionwavelength (e.g. in the red spectrum), a second LED in a second subpixeldesigned to emit a second peak emission wavelength (e.g. in the greenspectrum), and a third LED in a third subpixel designed to emit a thirdpeak emission wavelength (e.g. in the blue spectrum). A quantum dotlayer can be aligned over any of the LEDs to emit any of the first,second, or third peak emission wavelengths. In an embodiment, the firstLED has a peak emission wavelength between 340 nm and 420 nm, such asbetween 380 nm and 420 nm, and the quantum dot layer includes quantumdots designed to emit the first peak emission wavelength (e.g. in thered spectrum). Such an arrangement may allow for the integration ofquantum dot layers over efficient pump LEDs in which a pump LED peakemission wavelength is converted by the quantum dot layer to thesubpixel emission wavelength. Accordingly, this may allow for theintegration of pump LEDs into subpixels which may have a higherefficiency than what is possible with a comparable inorganicsemiconductor-based emissive LED at the same subpixel peak emissionwavelength. Similar arrangements can be made for other subpixels, inwhich the quantum dot layers are designed to emit at the peak emissionwavelengths of the subpixels, or alternatively the LEDs within thesubpixels may be designed to emit at the peak emission wavelengths ofthe supixels. Various combinations are possible.

In an embodiment, an array of quantum dot layers is embedded in a coverfilm of a wavelength conversion cover over LEDs mounted on the displaysubstrate. For example, the array of quantum dot layers can be formedwithin an array of cavities in the cover film. The cover film includingthe array of quantum dot layers can then be transferred to the displaysubstrate and aligned over the LEDs mounted on the display substrate.

In an embodiment, an array of quantum dot patches, each with a planartop surface, are aligned over LEDs mounted on a display substrate. Forexample, the array of quantum dot patches can be electrostaticallytransferred from a carrier substrate to the display substrate using anarray of electrostatic transfer heads.

In an embodiment, an array of quantum dot layers is within an array ofopenings formed in a planarization layer over an array of LEDs. Forexample, the planarization layer can formed on and patterned on thedisplay substrate, and the array of quantum dot layers then formedwithin an array of openings patterned in the planarization layer.Alternatively, the array of quantum dot layers can be formed on thedisplay substrate, followed by formation of the planarization layer. Inan embodiment the array of quantum dot layers is formed by depositionand patterning. For example, the quantum dot layers may be formed with aphotodefinable resist, either positive or negative.

Internal quantum efficiency (IQE) is a function of the quality andstructure of an LED, while external quantum efficiency (EQE) is definedas the number of photons emitted divided by the number of electronsinjected. EQE is a function of IQE and the light extraction efficiencyof the LED. At low operating current densities (also called injectioncurrent density, or forward current density) the IQE and EQE of an LEDinitially increases as operating current density is increased, thenbegins to tail off as the operating current density is increased in thephenomenon known as the “efficiency droop.” At lowest current densitiesthe efficiency may be low due to the strong effect of defects or otherprocesses by which electrons and holes recombine without the generationof light, called non-radiative recombination. As those defects becomesaturated radiative recombination dominates and efficiency is increased.An “efficiency droop” or gradual decrease in efficiency begins as theinjection current density surpasses a characteristic value. Ageneralized EQE curve for an inorganic semiconductor-based LED isillustrated in FIG. 1. Conventional inorganic semiconductor-based LEDsused for solid state lighting applications and backlighting applicationsare commonly driven at current densities well into the efficiency droopregion due to the requirement for high luminance (brightness), such as1,000,000 Nits. In accordance with embodiments, LEDs and quantum dotlayers may be integrated into display systems (e.g. mobile electronicdevices) designed for target luminance values such as 300 Nit for indoordisplay applications and up to about 2,000 Nit for outdoor displayapplications, which is well below the normal or designed operatingconditions for standard semiconductor-based LEDs.

In accordance with embodiments, display panels and display system aredescribed in which the LEDs may be micro LEDs having a maximum lateraldimension of 1 to 300 μm, 1 to 100 μm, 1 to 20 μm, or more specifically1 to 10 μm, such as 5 μm. At these dimensions the LEDs may be integratedinto display systems with a wide range of resolutions, for example,lower than 40 pixels per inch (PPI) to greater than 440 PPI, so long asthe subpixel pitch is less than the maximum width of the LEDs.Additionally, inorganic semiconductor-based LEDs may be characterizedhas having a higher efficiency and longer lifespan than common organicLEDs (OLEDs) commonly included in mobile electronics devices andtelevisions. Higher efficiency, in turn, may allow for lower energy orpower usage for the display system. In accordance with embodiments, theLEDs may operate around the maximum efficiency in their characteristicEQE curves, or even in the “pre-droop” region of the EQE curve.

Referring again to FIG. 1, in some embodiments, the characteristic EQEcurve of an LED may have a higher slope at the pre-droop region than inthe efficiency droop region. As a result, small fluctuations inoperating current density or variations in LED manufacturing andintegration processes may result in wide fluctuations in EQE of the LEDsand resultant brightness of the display system. Additionally, LEDsdesigned for different color emission may be fabricated using differentinorganic semiconductor-based systems. For example, blue or greenemitting LEDs may be fabricated using inorganic semiconductor materialssuch as, but not limited to, GaN, AlGaN, InGaN, AlN, InAlN, AlInGaN. Forexample, red emitting LEDs may be fabricated using inorganicsemiconductor materials such as, but not limited to, GaP, AlP, AlGaP,AlAs, AlGaAs, AlInGaP, AlGaAsP, and any As—P—Al—Ga—In. Variations in LEDmaterials and processing conditions may result in a differentcharacteristic EQE curve. For example, it has been observed that redemitting LEDs (e.g. including AlInGaP) have characteristic EQE curveswith lower maximum efficiency than blue emitting LEDs (e.g. includingAlGaN), and that the maximum efficiency of the EQE curve is shifted tothe right at higher current densities. Thus, red emitting LEDs withsimilar shape as corresponding blue emitting LEDs may be driven athigher currents than the corresponding blue emitting LEDs to achievesimilar brightness. It has additionally been observed that red emittingLEDs may be more susceptible to EQE shift due to operating temperaturevariations than the corresponding blue emitting LEDs. It is alsoanticipated that green emitting LEDs (e.g. including AlGaN) may sufferfrom a sustained efficiency gap compared to blue emitting LEDs withsimilar dimensions.

In one aspect, embodiments describe a display panel and system thatallows some control of emission profile from the display without havingto manipulate the LEDs to achieve a desired emission profile. Forexample, this may be accomplished by including less emissive LEDs withina display than there are subpixel emission colors within a pixel. Thiscan be accomplished by including the same pump LEDs for one or more, orall, of the subpixels within a pixel. In this manner, rather thandesigning different materials systems and integration schemes for LEDsof different emission colors for each subpixel, a subset or all of thesubpixels can include the same pump LED design with a known efficiency.

In some embodiments, QD layer thicknesses of 1 μm-100 μm and packingdensities of 1-60% may be utilized. Due to the LED dimensions and pitch,each QD layer or QD patch may have a limited footprint. The thickness ofthe QD layer within a subpixel may also be limited due to an aspectratio limitation (e.g. viewing angle and PPI) for the display panel. Insome embodiments, QD layer thicknesses of less than 20 μm, or even lessthan 5 μm are possible. Though, it is possible QD layers could bethicker, such as 50 μm or 100 μm. In some embodiments, the QD layer hasa sufficiently high QD packing density (e.g. at least 20% by volume, ormore specifically at least 40-50% by volume) in order to achievesufficient pump LED absorption, with mitigated pump LED transmission(bleeding) through the QD layer and mitigated re-absorption of QDemission by the QDs themselves.

In accordance with embodiments, a display panel includes a pixelarrangement of inorganic semiconductor-based LEDs including adown-converting QD layer over at least one LED. For example, in oneembodiment an RGB pixel may include a red emitting subpixel, a greenemitting subpixel, and a blue emitting subpixel. In one aspect, theinefficiencies related to an emitting LED for a specific color isreduced by providing a QD layer over a pump LED with a higherefficiency. For example, red emitting pixel may include a QD layer overa blue or deep blue emitting pump LED. Similarly, a QD layer may beformed over a blue or deep blue pump LED for down conversion into anumber of possible emission colors, including green, blue, and others.

The CIE 1931 color spaces adopted by the International Commission onIllumination (CIE) define quantitative links between colors in thevisible spectrum, and perceived colors in human color vision. Once suchcolor space is the CIE XYZ color space, which encompasses all colorsensations for a human standard observer. The CIE XYZ color spacedefines y as luminance, z as quasi-blue stimulation, and x as acombination of cone response curves chosen to be nonnegative. The CIEcolor matching functions are a numerical description of the chromaticresponse of a human standard observer (tri stimulus value) over thevisible spectrum. A CIE 1931 color matching function is reproduced inFIG. 2. As shown, the z plot of quasi-blue stimulation has a peak around448 nm.

In one aspect, embodiments describe the use of a UV emitting LED (e.g.between 340 nm and 380 nm) or deep blue emitting LED (e.g. between 380nm and 420 nm) as a pump LED with mitigated color erosion. As shown inFIG. 2, a human standard observer will have a lower chromatic responseof a deep blue emitting LED (e.g. between 380 nm and 420 nm) compared toa blue emitting LED closer to the peak tristimulus value around 448 nm.The chromatic response may be negligible at the upper UV range limit(e.g. from 340 to 380 nm). In other embodiments, the pump LED may have apeak emission wavelength that is shorter than the first absorption peakin the QD absorption spectrum (e.g. band edge). For example, this may beany wavelength below 500 nm.

In application, a QD layer may not down-convert 100% of light emittedfrom the underlying pump LED. Accordingly, it is possible some amount ofthe pump LED light may bleed through the QD layer and potentially erodethe color quality of the display. Referring now to FIG. 3, an exemplaryoverlay of an RGB display color space is provided over a CIE 1976uniform chromacity diagram (CIE 1976 UCS diagram). The RBG display colorspace is intended for exemplary purposes, and embodiments are notlimited to the specific RGB color space provided. In the particularillustration, simulation data is provided for two exemplary red subpixelconfigurations to illustrate the effect of pump LED leakage on colorquality. In the first sample illustrated as a dotted line in the closeup illustration, a red converter QD layer (centered at 625.5 nm peakemission wavelength) is formed over a pump LED with a peak emissionwavelength of 420 nm, and a presumed 4% leakage of the pump LED light.In the second sample illustrated as a solid line in the close upillustration, a red converter QD layer (centered at 625.5 nm peakemission wavelength) is formed over a blue emitting pump LED with a peakemission wavelength of 448 nm, and a presumed 4% leakage of the pump LEDlight. As shown, the resulting color coordinates of the RGB color spaceis shifted (or eroded) more with leakage of 448 nm light than for 420 nmlight. Thus, not only is the RGB color space eroded more significantlywith leakage of 448 nm light, the reproducible red color quality is alsoeroded more significantly with leakage of 448 nm light compared to 420nm light.

In one aspect, embodiments describe the use of an efficient deep blueemitting LED (e.g. between 380 nm and 420 nm, or lower) or UV emittingLED at the upper UV range (e.g. from 340 to 380 nm) as a pump LED. Asdescribed, variations in LED materials and processing conditions mayresult in a different characteristic EQE curve. For example, it has beenobserved that red emitting LEDs (e.g. including AlInGaP) havecharacteristic EQE curves with lower maximum efficiency than blueemitting LEDs (e.g. including AlGaN). Furthermore, changes incomposition within the same semiconductor systems can result indifferent emission wavelengths with different characteristic EQE curves.For example, the AlGaN semiconductor system can be used to fabricatedeep blue, blue, and green emitting LEDs. FIG. 4 is a graphicalillustration of peak EQE values for InGaN-based LEDs designed fordifferent color emission in accordance with an embodiment. In theembodiment illustrated in FIG. 4, an LED designed for peak emission at420 nm has a higher EQE than an LED designed for peak emission at 448nm. As a result, implementation of pump LEDs with peak emissionwavelengths between 380 nm and 420 nm, or lower, such as from 340 nm to380 nm, in accordance with embodiments may correspond to higherefficiency, and allow for lower energy or power usage for the displaysystem. In other embodiments, the pump LED may have a peak emissionwavelength that is shorter than the first absorption peak in the QDabsorption spectrum (e.g. band edge). For example, this may be anywavelength below 500 nm.

In one aspect, embodiments describe the use of a deep blue emitting LED(e.g. between 380 nm and 420 nm, or lower) or UV emitting LED at theupper UV range (e.g. from 340 to 380 nm) as a pump LED in order tofacilitate higher absorption by the QDs. It has been observed that lowerwavelengths of pump LED light, and hence higher energy, facilitates ahigher state in the band gap of a QD. As a result, lower pump LEDwavelengths may result in higher absorption coefficients of the QDlayers. In accordance with embodiments, this may allow for thinner QDlayers (facilitating conformance to pixel aspect ratios), lowerconcentrations of QDs in the QD layers, and lower pump leakage throughthe QD layers (less color desaturation).

FIG. 5 is a schematic illustration of the relationship of QD peakemission, QD absorption, and pump LED peak emission in accordance withan embodiment. As shown, QDs may generally have higher absorptioncoefficients of pump LED light at lower wavelengths, due to the higherenergy of pump light at lower wavelengths. For example, the QDabsorption coefficient of UV LED peak emission at the upper UV range(e.g. from 340 to 380 nm) or deep blue LED peak emission (e.g. between380 nm and 420 nm, or lower) may be greater than for blue LED peakemission at the low end of the blue spectrum near the peak tristimulusvalue (e.g. 448 nm+/−10 nm). Quantum dots may be selected to eliminateor reduce any overlap between the QD absorption spectrum and the QDemission spectrum. For example, a QD may be selected with a red or greenemission spectrum, with no or minimal overlap with the QD absorptionspectrum. This may allow for mitigated re-absorption of QD emitted lightby the QDs themselves, resulting in higher efficiency. In otherembodiments, the pump LED may have a peak emission wavelength that isshorter than the first absorption peak in the QD absorption spectrum(e.g. band edge). For example, this may be any wavelength below 500 nm.

Referring now to FIG. 6 an illustration is provided of a process fortransferring microdrivers and micro LEDs from carrier substrates to adisplay panel in accordance with an embodiment. Separate carriersubstrates are used for each micro LED 101 color and for themicrodrivers 111. One or more transfer assemblies 200 including an arrayof electrostatic transfer heads 202 can be used to pick up and transfermicrostructures from the carrier substrates (e.g., 102, 104, 106, 110)to the receiving substrate, such as display panel 120. In oneembodiment, separate transfer assemblies 200 are used to transfer anycombination of micro LED 101 colors and for the microdrivers 111. Thedisplay panel is prepared with distribution lines to connect the variousthe micro LED and microdriver structures. Multiple distribution linescan be coupled to landing pads and an interconnect structure, toelectrically couple the micro LEDs and the microdrivers, and to couplethe various microdrivers to each other. The receiving substrate can be adisplay panel 112 of any size ranging from micro displays to large areadisplays, or can be a lighting substrate, for LED lighting, or for useas an LED backlight for an LCD display. The micro LED and microdriverstructures are surface mounted on the same side of the substratesurface.

Bonds (e.g. from surface mounting) can be made using various connectionssuch as, but not limited to, pins, conductive pads, conductive bumps,and conductive balls. Metals, metal alloys, solders, conductivepolymers, or conductive oxides can be used as the conductive materialsforming the pins, pads, bumps, or balls. In an embodiment, heat and/orpressure can be transferred from the array of transfer heads tofacilitate bonding. In an embodiment, conductive contacts on themicrodriver and micro LEDs are thermocompression bonded to conductivepads on the substrate. In this manner, the bonds may function aselectrical connections to the microdriver chips and micro LEDs. In anembodiment, bonding includes bonding the conductive contacts on themicrodriver chips and micro LEDs with the conductive pads on the displaypanel. For example, the bonds may be intermetallic compounds or alloybonds of materials such as indium and gold. Other exemplary bondingmethods that may be utilized with embodiments of the invention include,but are not limited to, thermal bonding and thermosonic bonding. In anembodiment, the microdriver and micro LEDs are bonded to landing pads inelectrical connection with the distribution lines on the substrate toelectrically couple one or more micro LEDs, pixels of micro LEDs, to acorresponding microdriver.

FIG. 7 is a schematic top view illustration of a display panel inaccordance with an embodiment. As shown, the display panel 120 mayinclude a display substrate 112 including a display area 114 withinwhich the LEDs 101 are located, for example, in a matrix of pixels 116.Each pixel may include multiple subpixels that emit different colors oflights. In a red-green-blue (RGB) subpixel arrangement, each pixel mayinclude three subpixels that emit red light, green light, and bluelight, respectively. It is to be appreciated that the RGB arrangement isexemplary and that this disclosure is not so limited. Examples of othersubpixel arrangements that can be utilized include, but are not limitedto, red-green-blue-yellow (RGBY), red-green-blue-yellow-cyan (RGBYC), orred-green-blue-white (RGBW), or other subpixel matrix schemes where thepixels may have different number of subpixels.

One or more LEDs 101 may connect to a microdriver 111 that drives theone or more LEDs 101. For example, the microdrivers 111 and LEDs 101 maybe surface mounted on the display substrate 112. Display panel 120 mayinclude column driver(s) 124 (e.g. including column selection logic)and/or row driver(s) 122 (e.g. including row selection logic). Columndrivers 124 may include individual drivers for each column ofmicrodrivers 111. Row drivers 122 may include individual drivers foreach row of LEDs 101. A flex circuit 126 may be used for connection ofthe display panel 120 components to additional system components.

FIG. 8 is a schematic cross-sectional side view illustration of aportion of a display panel active area in accordance with an embodiment.The display substrate 112 may be a variety of substrates in accordancewith embodiments, the display substrate 112 may be a thin film substrate(TFT) substrate similar to conventional OLED display substrates. Thus,while the particular embodiments illustrated include an array ofmicrodrivers 111 mounted on the display substrate 112, this isexemplary, and embodiments do not necessarily require microdrivers 111mounted on the display substrate. Display substrate 112 may be rigid orflexible. For example, display substrate 112 may be formed of a varietyof materials such as polymer, glass, silicon, metal foil, etc. As showna bank layer 150 may optionally be formed on display substrate 112.Openings may be formed within the bank layer 150 to define subpixelareas for LEDs 101, and optionally for microdrivers 111 when the displaysubstrate does not include all of the driving circuits for operating theLEDs 101. LEDs 101 and microdrivers 111 may be bonded to bottomelectrode contact pads of the display substrate 112 with electricallyconductive bumps 136, e.g. solder bumps.

Still referring to FIG. 8 a passivation layer 160 may be formed over thedisplay substrate 112 and laterally around the LEDs 101 and optionallymicrodrivers 111. Passivation layer may be formed using a variety oftechniques. For example, passivation layer can be slot coated, slitcoated, or spin coated on the display substrate 112 to form a layer witha level top surface 161 across the display substrate. Passivation layer160 can be formed using other techniques such as ink jetting, physicalvapor deposition (PVD) or chemical vapor deposition (CVD). In anembodiment, the LED 101 includes a quantum well layer 144 between dopedlayers 140 (e.g. n-doped), 142 (e.g. p-doped) though the doping may bereversed. The passivation layer 160 may additionally provide stepcoverage for the deposition of a top electrode layer 170 such as indiumtin oxide (ITO) or poly(3,4-ethylenedioxythiophene (PEDOT). Thepassivation layer 160 may perform a variety of functions, includingsecuring the LEDs 101 and microdrivers 111 onto the display substrate112, passivating sidewalls of the LEDs 101 to protect against shortingbetween doped layers 140, 142, and acting as a leveling surface for theformation of the top electrode layer 170 without breaks due to changesin topography of the surface onto which the top electrode layer 170 isformed.

Quantum dots are semiconductor materials where the size of the structureis small enough (e.g. less than tens of nanometers) that the electricaland optical characteristics differ from the bum properties due toquantum conferment effects. For example, the emission properties ofquantum dots are related to their size and shape in addition to theircomposition. Fluorescence of quantum dots is a result of exciting avalence electron by absorbing a certain wavelength, followed by theemission of lower energy in the form of photons as the excited electronsreturn to the ground state. Quantum confinement causes the energydifference between the valence and conduction bands to change based onsize and shape of the quantum dot meaning that the energy and wavelengthof the emitted photos is determined by the size and shape of the quantumdot. The larger the quantum dot, the lower the energy of itsfluorescence spectrum. Accordingly, smaller quantum dots emit bluerlight (higher energy) and larger quantum dots emit redder light (lowerenergy). This allows size-dependent tuning of the semiconductorphotoluminescence emission wavelength throughout the visible spectrum,with a sharp emission spectrum and high quantum efficiency.

Examples of quantum dot materials include, but are not limited to,groups of II-VI, III-V, IV-VI semiconductor materials. Some exemplarycompound semiconductors include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, GaAs,GaP, GaAs, GaSb, HgS, HgSe, HgTe, InAs, InP, InSb, AlAs, AlP, AlSb. Someexemplary alloyed semiconductors include InGaP, ZnSeTe, ZnCdS, ZnCdSe,and CdSeS. Multi-core structures are also possible. Exemplary multi-coreconfigurations may include a semiconductor core material, a thin metallayer to protect the core from oxidation and to aid lattice matching,and a shell to enhance the luminescence properties. The shell mayfunction to absorb light at a specific spectrum that is different fromthe emission spectrum from the quantum dot. The core and shell layersmay be formed of the same material, and may be formed of any of theexemplary compound semiconductors or alloyed semiconductors listedabove. The metal layer often comprises Zn or Cd.

FIG. 9 is a schematic cross-sectional side view illustration of a barecore-shell quantum dot with bound ligands in accordance withembodiments. As shown, quantum dot 300 includes a core 302 and shell 304surrounding the core 302 as described above, and optionally a metallayer 301 between the core 302 and shell 304. In an embodiment, organicor inorganic ligands 306 are bound to the shell 304 surface. In anembodiment, the organic or inorganic ligands 306 are inside of anorganic (e.g. polymer) or inorganic (e.g. metal oxide or glass) matrixsurrounding the shell 304.

FIG. 10 is a schematic cross-sectional side view illustration of anano-encapsulated quantum dot in accordance with embodiments. As shown,quantum dot 300 illustrated in FIG. 10 includes a core 302 and shell 304surrounding the core 302, optional metal layer 301 between the core andshell, and a barrier layer 308 to provide surface protection fromchemical species, oxygen, and water. For example, the barrier layer 308may be a metal oxide. In accordance with embodiments, thenano-encapsulated quantum dots 300 illustrated in FIG. 10 can beembedded inside of an organic (e.g. polymer) or inorganic (e.g. metaloxide or glass) matrix, or used as neat particles to form a quantum dotlayer. In an embodiment, organic or inorganic ligands 306 are bound tothe barrier layer 308 surface, similarly as described with regard toFIG. 9. In an embodiment, the organic or inorganic ligands 306 areinside of an organic (e.g. polymer) or inorganic (e.g. metal oxide orglass) matrix surrounding the barrier layer 308.

FIG. 11 is a schematic cross-sectional side view illustration of amicro-encapsulated quantum dot in accordance with embodiments. As shown,quantum dots 300 (e.g. bare quantum dots as described above with regardto FIG. 9, or nano-encapsulated quantum dots as described above withregard to FIG. 10) are embedded inside a matrix 312 formed into a largenano or micro sized bead 310. The matrix 312 may be formed of a varietyof inorganic materials such as, but not limited to, metal oxide, glass,sol-gel (e.g. SiO₂, etc.) or organic materials such as, but not limitedto, acrylates, silicon, epoxy, and other polymeric materials.

Referring now to FIGS. 12A-12B one embodiment for a method of forming aquantum dot layer 400 is illustrated. As shown, QDs 300 or beads 310(both of which are referred to herein as particles) are functionalizedwith crosslinkable/polymerizable groups 305 (which may be on ligands).In order to form quantum dot layer 400, the functionalized quantum dots300 or beads 310 may be dispersed in a solvent (and any other chemicalspecies that may facilitate particle-particle crosslinking), coated intoa substrate 320, followed by driving off of the solvent resulting in adense packed quantum dot layer 400. Heat and/or light may then beapplied to drive a chemical reaction between the functional groups 305on the quantum dots 300 or beads 310 to cross-link them to one anotherto form liking moieties and create the cross-linked matrix 307 ofclose-packed quantum dots 300 or beads 310. The solvent and particlesolution can be applied to the substrate 320 in a variety of mannersincluding ink jetting, slot die coating, slit coating, screen printing,spin coating, etc. In an embodiment, it is the linking moieties betweenthe ligands bound to the surface of the particles (QDs 300 or beads 310)that form the cross-linked matrix 307. The QD layer 400 can then beplanarized to form a planar top surface 303, and optionally patternedinto discrete, separate patches.

Various click chemistries may be used to generate the cross-linkedmatrix 307, such as [3+2] cycloadditions (e.g. Huisgen 1,3-dipolarcycloaddition), thiol-ene click reactions, Diels-Alder reaction andinverse electron demand Diels-Alder reactions, [4+1] cycloadditionsbetween isonitriles (isocyanides) and tetrazines, nucleophilicsubstitution especially to small strained rings like epoxy and aziridinecompounds, carbonyl-chemistry-like formation of ureas, and additionreactions to carbon-carbon double bonds like dihydroxylation or thealkynes in the thiol-yne reaction.

In one example, the cross-linked matrix 307 may include a thiol-ynelinking moiety formed by cross-linking thiol and alkyne functionalgroups, e.g. alkyne hydrothiolation. In such an embodiment, theparticles are functionalized with a thiol and alkyne, or particlesfunctionalized with a thiol are mixed together with particlesfunctionalized with alkynes. The functional groups on the ligands reactto form the linking moiety resulting in the cross-linked matrix 307.

In one example, the cross-linked matrix 307 may be formed by acycloaddition reaction. In an embodiment, an isoxazoline orisoxazolidine linking moiety may be formed by a thermal cycloadditionreaction of a nitrone with an alkene. In an embodiment, the linkingmoiety may be formed by photochemical cycloaddition, such asdimerization of two alkenes facilitated by UV light. A variety ofadditional cycloaddition reactions are possible for forming linkingmoieties, such as the reaction of an azido and alykyne (e.g.azido-functionalized particles and cyclooctyne functionalizedparticles), Norbornene-tetrazine cycloaddition, or cycloaddition ofdibenzocyclooctynes and azides.

In one example, the cross-linked matrix 307 may be formed by acarbonyl-chemistry reaction, for example to form a urea, thiourea,aromatic hetercycle, oxide ether, hydrazone, or amide linking moiety. Inan embodiment, a urea is formed via carboxylic azides to produce anisocyanate, which reacts with an amine to form the urea.

FIGS. 13A-13B illustrated another method of forming a quantum dot layer400 in accordance with an embodiment. As shown, QDs 300 or beads 310(both of which are referred to herein as particles) may be dispersed ina solvent and coated into a substrate 320, followed by driving off ofthe solvent resulting in dense packed QDs particle film. The solvent andparticle solution can be applied to the substrate 320 in a variety ofmanners including ink jetting, slot die coating, slit coating, screenprinting, spin coating, etc. Following removal of the solvent, theparticle film may be coated with a film 309, such as an atomic layerdeposition (ALD) film that penetrates and fills in between theparticles, locking them together. The QD layer 400 can then beplanarized to form planar top surface 303, and optionally patterned intodiscrete, separate patches. In another embodiment, the dense packed QDparticle film could be filled in with a spin-on-glass (sol-gel) that isthen cross-linked (e.g. upon exposure to heat). In order to mitigateshrinkage that may occur due to removal of solvent and densification ofthe film from cross-linking, the solvent and cure can be performedmultiple times. The QD layer 400 can then be planarized to form planartop surface 303, and optionally patterned into discrete, separatepatches.

Embodiments are not limited to dense packed QD layers 400 illustratedand described with regard to FIGS. 12A-13B. For example, QDs 300 orbeads 310 can be dispersed within a transparent matrix material, such asglass or polymer (e.g. acrylic). In a embodiment, QDs 300 or beads 310are dispersed in a photodefinable resist, which can be positive ornegative. Other materials may also be dispersed within the matrixmaterial such as a light scattering agent such as TiO₂ or Al₂O₃particles. Such light scattering particles may have the effect ofincreasing quantum dot efficiencies by increasing scattered pump LEDlight within the QD layer 400 and interaction with the quantum dots.This may be accomplished by tuning the size of the light scatteringparticles to primarily scatter the pump LED light peak emissionwavelength, will much less to negligible scattering of the QD peakemission wavelength.

QD layers 400 in accordance with embodiments may be integrated into avariety of configurations, and assume a variety of form factors. In someembodiments, QD layer 400 thicknesses of less than 20 μm, or even lessthan 5 μm are possible. In some embodiments, the QD layer has asufficiently high QD packing density (e.g. at least 20% by volume, ormore specifically at least 40-50% by volume) in order to achievesufficient pump LED absorption, with mitigated pump LED transmission(bleeding) through the QD layer and mitigated re-absorption of QDemission by the QDs themselves. As used herein, the term packing densityis refers to the QD particle components (e.g. inorganic components) suchas core 302, metal layer 301, shell 304, and barrier layer 308. Ligands306, and consequently the cross-linked matrix 307 or film 309 are notparticle components within the meaning of packing density for determinevolume loading of the QDs within a QD layer.

Referring now to FIGS. 14A-14E various LED and quantum dot layerarrangements in a RGB pixel system are illustrated in accordance withembodiments. It is to be appreciated that the RGB pixel system isexemplary and the embodiments are not so limited. Examples of otherpixel systems that can be utilized include, but are not limited to,red-green-blue-yellow (RGBY), red-green-blue-yellow-cyan (RGBYC),red-green-blue-white (RGBW), or other pixel systems where the pixelshave a different number of subpixels.

In the embodiment illustrated in FIG. 14A, a pixel 116 includes a blueemitting LED 101, a green (G) emitting LED 101, and a blue (B) or deepblue (DB) emitting pump LED 101. A quantum dot layer 400 is formed overthe (e.g. deep blue) pump LED 101, and optionally over the green mittingLED 101. The quantum dot layer 400 may include red-emitting QDs in theembodiment illustrated for an RGB pixel. Referring briefly back to FIG.5, in an embodiment, the QDs in the quantum dot layer 400 have anabsorption band spectrally shifted to lower wavelengths with littleabsorption in the green or red spectrums. Likewise the pump LED peakemission is shifted to a lower wavelength (e.g. deep blue). This mayallow for very low re-absorption, and better efficiency. Where there islimited to no overlap between the QD absorbance spectrum and the greenor red emitting LED spectrums, it is possible that the quantum dot layer400 can overlap both the deep blue pump LED and an adjacent emissive LED(e.g. green). This may allow for a greater footprint, and height of theQD layer 400 alleviating potential density-related challenges for adisplay with high PPI.

In an embodiment, a scattering agent is included within the QD layer400. For example, the scattering agent could be particles (e.g. TiO₂ orAl₂O₃) designed to scatter primarily the pump LED light to increaseinteraction of the pump LED light with the QDs and mitigate leakage ofthe pump LED light. To mitigate pump LED leakage, a color filter layer410 can optionally be formed over the QD layer 400 to absorb wavelengthsat the pump LED emission spectrum (e.g. deep blue filter). For example,the color filter layer 410 may include a pigment or dye dispersed in atransparent matrix material.

Referring now to FIGS. 14B-14E, additional LED and quantum dot layerarrangements in a RGB pixel system are illustrated in accordance withembodiments. While specific arrangements utilizing a deep blue emittingpump LED are shown, embodiments are not so limited, and a variety ofother pump LEDs may be used. For example, any of the DB LEDs illustratedin FIGS. 14A-14D may be replaced with UV LEDs. In some embodiments, pumpLEDs with an emission wavelength less than 500 nm are utilized. In theembodiment illustrated in FIG. 14B, a QD layer 400 (e.g. with redemitting QDs) is formed over a deep blue emitting pump LED 101, whilegreen emitting and blue emitting LEDs 101 are bare (i.e. with nooverlying QD layer). In the embodiment illustrated in FIG. 14C, a QDlayer 400 (e.g. with red emitting QDs) is formed over a deep blueemitting pump LED 101, a QD layer 400 (e.g. with green emitting QDs) isformed over a deep blue emitting pump LED 101, while a blue emitting LED101 is bare (i.e. with no QD layer). In the embodiment illustrated inFIG. 14D, a QD layer 400 (e.g. with red emitting QDs) is formed over adeep blue emitting pump LED 101, a QD layer 400 (e.g. with greenemitting QDs) is formed over a deep blue emitting pump LED 101, and a QDlayer 400 (e.g. with blue emitting QDs) is formed over a deep blueemitting pump LED 101. In the embodiment illustrated in FIG. 14E a QDlayer 400 (e.g. with red emitting QDs) is formed over a blue emittingLED 101, while green emitting and blue emitting LEDs 101 are bare (i.e.with no overlapping QD layer). In such an arrangement, only two LEDdonor wafers are used to form the pixel arrangement.

In the particular embodiments, illustrated in FIGS. 14A-14E, the QDlayers 400 are illustrated as dome shaped. For example, this may beaccomplished by ink jetting individual QD layers 400 over the LEDs 101.However, embodiments are not limited to the specific shape andarrangement of QD layers 400 illustrated in FIGS. 14A-14E, and therelationships of QD layer peak emission with LED 101 peak emissionwavelengths within pixels can be integrated into a number of alternativestructures, such as a wavelength conversion cover arrangement, QD patcharrangement, or QD patterning on the display substrate.

In the following description with regard to FIGS. 15-21C various displayconfigurations are described and illustrated in accordance withembodiments for integrating a pump LED with overlying QD layer, and anemissive LED with no overlying QD layer. For example, the integrationschemes may be related to a wavelength conversion cover arrangement, QDpatch arrangement, or QD patterning on the display substrate. While onlytwo LEDs are described and illustrated, it is to be appreciated thatembodiments are not so limited and that the embodiments of FIGS. 15-21Care compatible with other embodiments described herein, including theLED and QD layer various described and illustrated with regard to FIGS.14A-14E.

Additionally, various configurations are illustrated in FIGS. 15-21C inwhich a Bragg reflector layer 440 (e.g. to reflect a peak emissionwavelength of a quantum dot layer 400) may optionally be included overeither or both of a pump LED 101 and emissive LED 101, and a Braggreflector layer 465 (e.g. to reflect a peak emission wavelength of apump LED 101) may optionally be included over either or both of aquantum dot layer 400 (e.g. over a pump LED 101) and over a fillmaterial 402, for example (e.g. over an emissive LED 401). It is to beunderstood that the Bragg reflector layers 440, 465 can be patterned toform openings over one or more LEDs 101 and subpixels. In practiceeither of the Bragg reflector layers 440, 465 may be patterned toincrease performance. For example, in an embodiment the pump LED 101 isa blue emitting LED. In such a configuration, a Bragg reflector layer465 may be formed over a quantum dot layer 400 (e.g. for red emission,red subpixel) and optionally patterned so that it does not cover (e.g.is not formed over) a blue emissive LED 101 (e.g. blue subpixel). In anembodiment, the pump LED 101 is a UV emitting LED or deep blue emittingLED, and the Bragg reflector layer 465 is formed over all LEDs 401 (pumpand emissive) within a pixel, though the Bragg reflector layer 465 mayoptionally be patterned. These two examples are illustrative of numerouscombinations that are envisioned. In interest of not obscuring thepresent embodiments, the Bragg reflector layers 440, 465 are illustratedin FIGS. 15-21C as being formed over both the exemplary pump LED andemissive LED, however, this is optional and embodiments are not solimited.

Referring now to FIG. 15 a schematic cross-sectional side viewillustration is provided of a portion of a display panel in accordancewith an embodiment. The display panel 120 includes a display substrate112, an array of LEDs 101 mounted on the display substrate 112 in anarray of pixels (for example, as described and illustrated with regardsto FIGS. 6-8). As shown, bank structures 150 may optionally be formedaround the LEDs 101. LEDs 101 may optionally include a reflective mirror146 for direction of light emission. Bank structures 150 may optionallyinclude a reflective mirror 152 for direction of light emission. Asshown, the LEDs 101 are embedded in a passivation layer 160 laterallysurrounding sidewalls of the LEDs 101 and above a quantum well layer ofthe LEDs. A top electrode layer 170 is formed over the array of LEDs101.

A wavelength conversion cover 490 is transferred to the displaysubstrate 112 so that the array of quantum dot layers 400 are alignedover an array of LEDs 101 mounted on the display substrate. As shown,the wavelength conversion cover 490 includes an array of quantum dotlayers 400 embedded in a cover film 450 (e.g. polymer, glass, etc.). Inan embodiment, the wavelength conversion cover 490 may be secured overall of the pixels in the display area 114 (see FIG. 7) of the displaypanel 120. The wavelength conversion cover 490 may be attached to thedisplay substrate 112, and hermetically sealed using seal 480 such asglass frit, epoxy, glass to glass laser seal, etc. or not hermeticallysealed using seal 480 such as epoxy, adhesive, etc.

LEDs 101 may be pump LEDs with a QD layer 400 arranged over the LED 101(as shown in the left subpixel), or emissive LEDs with no QD layer 400arranged over the LED 101 (as shown with the right subpixel). Forexample, each QD layer 400 may be contained within a cavity (see 455FIG. 16B) formed in a bottom surface (see 451 FIG. 16A) of the coverfilm 450. Where a QD layer 400 is not aligned over an emissive LED 101,a fill material 402 may optionally be formed contained within a cavityaligned over the emissive LED 101. For example, the fill material 402may include a scattering agent to scatter light emitted from theunderlying LED 101 and distribute light emitting from the subpixelsimilarly as the subpixel including the QD layer 400. In an embodiment,light guides 452 may be formed in the cover film 450 over the cavities.The light guides 452 may be characterized by a higher refractive indexthan a bulk of the cover film 450 to contain the light. A barrier layer430, e.g. atomic layer deposition (ALD) Al₂O₃ film, may optionally beformed on the cover film 450 to seal the QD layers 400. A Braggreflector layer 440 (e.g. composed of multiple thin layers of dielectricmaterial), which may also function as a barrier layer 430, mayoptionally be formed on the cover film 450. The Bragg reflector layer440 is positioned under the QD layers 400 and aligned over the pump LEDs101 in the embodiment illustrated. In this manner, the Bragg reflectorlayer 440 is transparent to the peak emission wavelength of the pumpLEDs 101, and reflective to the QD layers 400. Separate Bragg reflectorlayers 440 may be formed where different QD layers 400 are included. Forexample, green emitting QD layers 400 and red emitting QD layers 400 mayhave different corresponding Bragg reflector layers 440.

In the embodiment illustrated, a single Bragg reflector layer 440 may beformed across the subpixel including the QD layer 400 and fill material402. For example, in such an embodiment, the Bragg reflector layer 440may be transparent to the peak emission wavelengths for both the pumpand emissive LEDs 401. Alternatively, a Bragg reflector layer 440 maynot be formed across the fill material 402. In an embodiment utilizing asingle pump LED 101 peak emission wavelength, a single Bragg reflectorlayer 440 may be included over each pump LED 101 within a pixel.

By way of example, and for illustrational purposed the arrangements ofLEDs 401 illustrated in FIG. 15 may include a pump LED 101 designed toemit a peak emission wavelength between 340 nm and 420 nm (e.g. between380 nm and 420 nm), and an emissive LED 101 designed to emit a peakemission wavelength above 438 nm (e.g. blue, green, red, etc.).

Quantum dot layer 400 is aligned over the pump LED 101. Quantum dotlayer 400 includes quantum dots designed to emit a peak emissionwavelength above 438 nm. A color filter layer 410 may optionally beformed in cavity and over the quantum dot layer 400 to absorb the peakemission wavelength of the pump LED 101 (i.e. to mitigate bleeding ofthe pump LED). In an embodiment, color filter layer 410 is a UV-cutabsorber with a cut-off wavelength e.g. at 380 nm or 400 nm to absorbthe pump wavelength while being transparent to all visible wavelengths.Fill material 402 may optionally be aligned over the emissive LED 101.In an embodiment, a cavity is not formed in region of the cover film 450aligned over the emissive LED 101.

In an embodiment, a Bragg reflector layer 465 (e.g. composed of multiplethin layers of dielectric material) may be formed over the quantum dotlayer 400, and underneath the color filter layer 410, if present. TheBragg reflector layer 465 may be reflective of the peak emissionwavelength of the pump LEDs 101, and transparent to the peak emissionwavelength of the QD layers 400. In this manner, the pathlength of thepump LED 101 through the QD layer 400 may be increased, potentiallyincreasing efficiency of the QD layers 400.

A method of forming the wavelength conversion cover 490 is illustratedand described with regard to FIGS. 16A-16D. As shown, a cover film 450(e.g. glass or polymer substrate) may optionally be attached to asupport substrate 500, for example, with an optional adhesive film 502.In a specific embodiment an amorphous hydrogenated silicon film (Si:H)can be formed, for example by plasma enhanced chemical vapor deposition(PECVD) to a thickness, for example of 200 nm. A glass or polymer coverfilm 450 may then be coated onto the (Si:H) film. Cavities 455 may beformed in what will be the bottom surface 451 of the cover film 450using a variety of available techniques include lithography and etching,embossing, laser ablation/evaporation, etc. Cavities 455 mayadditionally be lens shaped to aid light extraction and control light.In the embodiment illustrated, the cavities do not extend all the waythrough a thickness of the cover film. In such a configuration, thecover film 450 may be formed of a transparent material to allow lighttransmission through a portion of the bulk material above the cavities455 in the display panel. A black matrix layer 420 may optionally beformed and patterned on the bottom surface 451 of the cover film 450before or after forming the cavities 455, for example to decreaseambient light reflection.

Following the formation of cavities 455, a color filter layer 410 andBragg reflector layer 465 may optionally be formed in and along thewalls of one or more cavities 455 in a pixel. In an embodiment, the sameBragg reflector layer 465 may be formed along the walls of multiplecavities 455 corresponding to different subpixels within a pixel. TheBragg reflector layer 465 may be designed to be reflective of the peakemission wavelength of a pump LED, while being transparent to the QDlayers 400 and/or emissive LEDs 101. In an embodiment, the same colorfilter layer 410 is formed along the walls of multiple cavities 455corresponding to different subpixels within a pixel. The color filterlayer 410 may be designed to absorb the peak emission wavelength of apump LED, while being transparent to the QD layers 400 and/or emissiveLEDs 101. In an embodiment, color filter layer 410 is a UV-cut absorberwith a cut-off wavelength e.g. at 380 nm or 400 nm to absorb the pumpwavelength while being transparent to all visible wavelengths.Accordingly, in a configuration using multiple quantum dot layers 400for different subpixels, and the same pump LED emission wavelength forthose subpixels, may include the same color filter layer 410 and Braggreflector layer 465 in those respective subpixels. In an embodiment, acolor filter layer 410 and Bragg reflector layer 465 are not included ina cavity 455 that will be aligned over an emitting LED, particularly ifthe peak emission wavelength of the emitting LED is absorbed by thecolor filter layer 410 or reflected by the Bragg reflector layer 465. Insome instances, it may be economical to leave the color filter layer 410and Bragg reflector layer 465 over an emitting LED where the colorfilter layer 410 and Bragg reflector layer 465 were designed to interactwith a pump LED that has a primary emission wavelength that is differentthan that for the emitting LED.

Following the formation of cavities 455, and optionally color filterlayer(s) 410 and Bragg reflector layer 465, one or more arrays of QDlayers 400, and optionally fill material 402, are formed within thecavities 455 in a pixel. Exemplary manners of formation include coating(e.g. slot die, slit coating, screen printing, etc.) and dispensing(e.g. ink-jet printing, micro dispense, etc.). Exemplary arrangements ofQD layers 400 within an RGB pixel system are illustrated in FIGS.14A-14E. In addition to the formation of QD layers 400, fill material402 may be similarly formed within cavities 455 to be aligned over bareLEDs 101. Following the formation of QD layer(s) 400 and optionally fillmaterial 402, a barrier layer 430 and/or Bragg reflector layer 440 maybe formed.

In an embodiment, a laser lift off method is used to release the coverfilm 450 including the embedded QD layers 400, and optionally embeddedfill material 402, from the carrier substrate 500.

Referring now to FIG. 17 a schematic cross-sectional side viewillustration is provided of a portion of a display panel in accordancewith an embodiment. The display panel illustrated in FIG. 17 containsmany similarities as the one previously illustrated and described withregard to FIG. 15. The display panel 120 includes a display substrate112, an array of LEDs 101 mounted on the display substrate 112 in anarray of pixels (for example, as described and illustrated with regardsto FIGS. 6-8). A wavelength conversion cover 490 is transferred to thedisplay substrate 112 so that the array of quantum dot layers 400 arealigned over an array of LEDs 101 mounted on the display substrate. Asshown, the wavelength conversion cover 490 includes an array of quantumdot layers 400 embedded in a cover film 450 (e.g. polymer, glass, etc.).In an embodiment, the wavelength conversion cover 490 may be securedover all of the pixels in the display area 114 (see FIG. 7) of thedisplay panel 120. The wavelength conversion cover 490 may be attachedto the display substrate 112, and hermetically sealed using seal 480such as glass frit, epoxy, glass to glass laser seal, etc. or nothermetically sealed using seal 480 such as epoxy, adhesive, etc. Onedifference from the embodiment illustrated in FIG. 17 compared to theembodiment illustrated in FIG. 15 is in the design for controlling lightemission profile. For example, cavities may optionally be formedcompletely through the cover film 450. The cavities may additionallyoptionally be lined with a mirror layer 440 rather than color filterlayer. The cavities may additionally optionally be partially filled witha QD layer 400 or fill material 402.

A method of forming the wavelength conversion cover 490 of FIG. 17 isillustrated and described with regard to FIGS. 18A-18D. As shown, acover film 450 (e.g. glass or polymer substrate) may optionally beattached to a support substrate 500. Cavities 455 are etched into thecover film 450 using a suitable etching technique, such as holographicetching. The shape and profile of the cavities 455 can be changed tocontrol emission profile of the respective subpixels. In the embodimentillustrated in FIG. 18A, the cavities 455 are etched completely throughthe cover film 450. In such a configuration, the cover film 450 may beformed of a transparent material, or optionally opaque material to limitlight transmission to the areas defined by cavities 455. A black matrixlayer 420 may optionally be formed on the cover film 450 prior to orafter etching cavities 455.

Following the formation of cavities 455, a mirror layer 440 may beformed in and along the walls of one or more cavities 455 in a pixel. Inan embodiment, the mirror layer 440 is formed within all cavities 455.The mirror layer 440 may be designed to reflect light from QD layers, aswell as from emissive LEDs 101 if present. One or more QD layers 400 maybe from in cavities 455 that will be aligned over pump LEDs 101. In theembodiment illustrated, a fill material 402 may optionally be formed inthe cavities 455 that will be aligned over emissive LEDs 101. DifferentQD layers 400 may be formed over different subpixels designed fordifferent color emission.

Referring now to FIG. 18C, a secondary fill material 460 may then beformed in any remaining open space within cavities 455. For example,secondary fill material 460 may be characterized by a higher refractiveindex than cover film 450. The secondary fill material 460 may alsofunction as a leveling material for the formation of additional layers.For example, secondary fill material 460 may have a top surface that iscoplanar with a top surface of the black matrix layer 420 or cover film450. Exemplary manners of forming the QD layers 400, fill material 402,and secondary fill material 460 include coating (e.g. slot die, slitcoating, screen printing, etc.) and dispensing (e.g. ink-jet printing,micro dispense, etc.). Exemplary arrangements of QD layers 400 within anRGB pixel system are illustrated in FIGS. 14A-14E. Following theformation of QD layer(s) 400, optional fill material 402, and optionalsecondary fill material 460, a Bragg reflector layer 465 and a colorfilter layer 410 may optionally be formed over the available surface. Inan embodiment, the Bragg reflector layer 465 is designed to reflect thepeak emission wavelength of the pump LEDs, and be transparent to the QDlayers 400 and optionally other emissive LEDs. In an embodiment, thecolor filter layer 410 is designed to absorb the peak emissionwavelength of the pump LEDs 101. In an embodiment, color filter layer410 is a UV-cut absorber with a cut-off wavelength e.g. at 380 nm or 400nm to absorb the pump wavelength while being transparent to all visiblewavelengths.

Referring now to FIG. 18D, the carrier substrate 500 is released, andthe opposite side of the structure is attached to a second carriersubstrate 600. A black matrix layer 420 may optionally be formed overthe cover film 450. Alternatively, a black matrix layer 420 could havebeen formed on the carrier substrate 500 prior to the cover film 450,and cavities 455 patterned through the cover film 450 and black matrixlayer 420. In the embodiment illustrated, a barrier layer 430 and/orBragg reflector layer 440 may optionally be formed. The second carriersubstrate 600 may be released, resulting in the wavelength conversioncover 490 illustrated in FIG. 17.

Referring now to FIGS. 19A-19E a method of forming a display panelincluding quantum dot patches 455 is illustrated in accordance withembodiments. Referring to FIG. 19A, a QD layer 400 is formed on acarrier substrate 500. The QD layer 400 may include QDs embedded in amatrix material such as an inorganic (e.g. metal oxide, glass, etc.) ororganic (e.g. polymer such as acrylate, epoxy, silicone, etc.). The QDlayer 400 may also be formed similarly as previously described withregard to FIGS. 12A-13B. The QD form factor may be any of the QD formfactors previously described, such as bare QDs, nano-encapsulate QDs,micro-encapsulated QDs, etc.

The QDs can emit any wavelength of light when pumped with any wavelengthof light lower (and higher energy) than the QD band gap. In anembodiment, a Bragg reflector layer 440 (e.g. to reflect the QDemission) is optionally formed on the carrier substrate 500 prior toforming the QD layer 400. In an embodiment, a Bragg reflector layer 465(to reflect pump LED emission) is optionally formed over the QD layer400. In an embodiment, a color filter layer 410 (e.g. to absorb the pumpLED light) is optionally formed over the QD layer 400. In an embodiment,color filter layer 410 is a UV-cut absorber with a cut-off wavelengthe.g. at 380 nm or 400 nm to absorb the pump wavelength while beingtransparent to all visible wavelengths.

Referring to FIG. 19B the layers formed on the carrier substrate 500 arepatterned to form discrete QD patches 445 using a suitable techniquesuch as etching, saw, laser, etc. The discrete QD patches 445 may thenbe poised for pick up and transfer to a display substrate 112 similarlyas the LEDs 101 and optionally microdrivers 111 as previously described.In an embodiment, a method of forming a display panel includeselectrostatically transferring an array of LEDs 101 from an LED carriersubstrate to a display substrate 112, and electrostatically transferringan array of QD patches 445 from a QD patch carrier substrate 500 to thedisplay substrate 112, and aligning the array of QD patches 445 over thearray of LEDs 101. The arrangement of LEDs 101 and QD patches 445including QD layers 400 may be any of those arrangements previouslydescribed with regard to FIGS. 14A-14E, amongst other possiblearrangements.

Referring to FIG. 19C, in an embodiment a fill material patch 447including fill material 402 is transferred to the display substrate, andaligned over emissive LED 101. For example, the fill material 402 may besimilar to previously described fill material, and may includescattering particles. In accordance with embodiments, the QD patches 445and optional fill material patches 447 include planar top surfaces 446,449, respectively. The planar top surfaces may be useful forelectrostatic transfer operations, where a planar top surfacefacilitates uniform contact with the electrostatic transfer heads andthe patches.

As shown in FIG. 19D, following the transfer of QD patches 445 andoptionally fill material patches 447, a planarization layer 470 mayoptionally be formed around the array of QD patches 445, and optionallyfill material patches 447 on the display substrate 112. A black matrixlayer 420 may optionally be formed over the planarization layer 470 toreduce ambient light reflection.

In the embodiment illustrated in FIG. 19E, fill material patches 447 arenot aligned over the emissive LEDs 101, and the planarization layer 470is formed directly over the emissive LEDs 101. In an embodiment, theplanarization layer 470 is formed of the fill material 402, and mayinclude scattering particles.

In an embodiment, a display panel includes a display substrate 112, anarray of LEDs mounted on the display substrate in an array of pixels,and an array of quantum dot patches 445 aligned over the array of LEDs101, where each quantum dot patch 445 in the array of quantum dotpatches includes a planar top surface 446. The quantum dot patches 445may include multiple layers, such as a QD layer 400, an optional colorfilter layer 410 over the QD layer 400, and an optional Bragg reflectorlayer 440 underneath the QD layer 400. In some embodiments, the array ofLEDs 101 are pump LEDs designed to emit a peak emission wavelengthbetween 340 nm and 420 nm (e.g. between 380 nm and 420 nm). A secondarray of LEDs 101 may be mounted on the display substrate 112 within thearray of pixels. As shown in FIGS. 19D and 19E, the second array of LEDs101 may be emissive LEDs and may be designed to emit a peak emissionwavelength above 438 nm. In such a configuration, a QD patch 445 is notaligned over the second array of LEDs. In an embodiment, a second arrayof QD patches 445 is aligned over the second array of LEDs 101. Forexample, the second array of QD patches 445 may be designed to emit adifferent primary wavelength than the first array of QD patches 445. Inan embodiment the second array of LEDs are pump LEDs 101 designed toemit a peak emission wavelength between 340 nm and 420 nm (e.g. 380 nmand 420 nm).

In the embodiments illustrated in FIGS. 19A-19E, the QD patches 445 wereillustrated as including Bragg reflector layers 440, 465 and colorfilter 410. However, this is exemplary, and these layers may be includedin the structure outside of the QD patches 445. For example, the Braggreflector layer 440 may be formed over the LEDs 101 prior totransferring the QD patches 445. Additionally, Bragg reflector layer 440and color filter 410 may be formed after the planarization layer 470.For example, these layers may also be formed over the planarizationlayer 470.

FIGS. 19F-19G are schematic cross-sectional side view illustrations ofmethods of forming a display panel including layer transfer inaccordance with embodiments. In an embodiment illustrated in FIG. 19F,rather than transferring QD patches 445 individually, they may betransferred together in a layer transfer process, similar to waferbonding. As described in the above paragraph, optional layers such asBragg reflector layers 440, 465 and color filter may be included in eachQD patch, or alternatively formed as a layer to be transferred, asillustrated in FIG. 19G.

Referring now to FIGS. 20A-20E, methods of patterning QD layers 400 onthe display substrate 112 are illustrated in accordance withembodiments. Referring to FIG. 20A, a display substrate 112 with mountedLEDs 101 and microdrivers 111 is illustrated after the formation of topelectrode layer 170. A Bragg reflector layer 440 is optionally formedover the top electrode layer 170. Bragg reflector layer 440 may beformed of non-electrically conductive materials, and may additionallyelectrically passivate the top electrode layer 170 from any overlyingelectrically conductive layers.

QD layers 400 may then be formed over the pump LEDs 101 and the optionalBragg reflect layers 440. In one embodiment illustrated in FIGS.20A-20B, the planarization layer 470 is applied over the displaysubstrate, and patterned to form openings 475 over the pump LEDs 101.The QD layers 400 may then be applied within the defined openings. Fillmaterial 402 layers may optionally be similarly formed over the emittingLEDs 101. In one embodiment illustrated in FIGS. 20F-20H, the QD layers400 are formed over the pump LEDs 101 followed by application of aplanarization layer 470. For example, a global QD film can be formedover the substrate, followed by etching away portions of the QD film toachieve QD layers 400 aligned over the pump LEDs 101. In an embodiment,the global QD film is a photodefinable resist material (e.g. positive ornegative) that is patterned to form QD layers 400. Fill material 402layers may optionally be similarly formed over the emitting LEDs 101.

Following the formation of QD layers 400, and optionally fill material402 layers and planarization layer 470 one or more Bragg reflectorlayers 465, color filter layers 410 and/or a black matrix layer 420 mayoptionally be formed. A barrier layer 430 (e.g. ALD Al₂O₃ film) mayoptionally be formed prior to the Bragg reflector layer 465, colorfilter 410 and/or black matrix layer 420. In the embodiment illustrated,the same Bragg reflector layer 465 and the same color filter layer 410span over the subpixel including a pump LED 101 as well as a subpixelincluding an emissive LED 101. In such an embodiment, the Braggreflector layer 465 is designed to reflect the peak emission wavelengthof the pump LED 101 and the color filter layer 470 is designed to absorbthe peak emission wavelength of the pump LED 101. In another embodiment,the Bragg reflector layer 465 and/or the color filter layer 410 do notspan over the emissive LED 101.

Referring now to FIG. 20D, in an embodiment the planarization layer 470may also be an opaque material, or black matrix material. In anembodiment, an insulating layer such as a Bragg reflector layer 440 maybe formed between the planarization layer 470 and top conductive contactlayer 170 to prevent electrical shorting of the top conductive contactlayer 170 through conductive particles (e.g. for black matrix) in theplanarization layer 470.

Referring now to FIG. 20E, rather that forming discrete fill material402 layers over the emissive LEDs 101, in an embodiment theplanarization layer 470 may also be formed of the fill material 402, andmay include scattering particles.

In an embodiment, a display panel 120 includes an arrangement of LEDs101 mounted on a display substrate 112 such as that illustrated in FIGS.20A-20H, and in an array of pixels. A planarization layer 470 is overthe array of LEDs 101, and the planarization layer includes an array ofopenings 475 aligned over the array of LEDs 101. An array of QD layers400 is within the array of openings 475 aligned over the array of LEDs101. A top surface of each QD layer 400 in the array of QD layers may belevel with a top surface of the planarization layer 470 (e.g. they mayhave been planarized). A Bragg reflector layer 440 may be formed overthe array of LEDs 101 and underneath the planarization layer 470 and thearray of QD layers 400. A Bragg reflector layer 465 may be formed overthe array of QD layers 400 and the planarization layer 470.

FIGS. 21A-21C illustrate a method of patterning QD layers 400 on thedisplay substrate 112 in accordance with an embodiment. Referring toFIG. 21A, a display substrate 112 with mounted LEDs 101 and microdrivers111 is illustrated after the formation of top electrode layer 170. Aplanarization layer 470 is then formed on the display substrate 112 overthe array of LEDs 101, top electrode layer 170, and optionallymicrodrivers 111. In the particular embodiment illustrated, theplanarization layer is formed of a transparent material. Theplanarization layer is patterned to form openings 475 over the pump LEDs101, and optionally emissive LEDs 101. As shown, the openings 475 maynot extend through an entire thickness of the planarization layer 470. ABragg reflector layer 440 is optionally formed over the planarizationlayer 170 and within the openings 475.

Referring to FIG. 21B, QD layers 400 may then be formed within theopenings 475 over the pump LEDs 101 and the optional Bragg reflectlayers 440. Fill material 402 may optionally be similarly formed withinthe openings 475 over the emitting LEDs 101. Following application ofthe QD layers 400 and optional fill material 402, the stack structuremay be planarized. For example, this may result in a planar top surfaceincluding a planar top surface of the QD layers 400, optional fillmaterial 402, and the planarization layer 470 and/or Bragg reflectorlayer 440. As previously described, one or more Bragg reflector layers465, color filter layers 410 and/or a black matrix layer 420 mayoptionally be formed as illustrated in FIG. 21C. A barrier layer 430(e.g. ALD Al₂O₃ film) may optionally be formed prior to the Braggreflector layer 465, color filter 410 and/or black matrix layer 420.

In an embodiment, a display panel 120 includes an arrangement of LEDs101 mounted on a display substrate 112 such as that illustrated in FIGS.21A-21C, and in an array of pixels. A planarization layer 470 is overthe array of LEDs 101, and the planarization layer includes an array ofopenings 475 aligned over the array of LEDs 101. An array of QD layers400 is within the array of openings 475 aligned over the array of LEDs101. A top surface of each QD layer 400 in the array of QD layers may belevel with a top surface of the planarization layer 470 (e.g. they mayhave been planarized). A Bragg reflector layer 440 may be formed overthe planarization layer 470, where the array of QD layers 400 is overthe Bragg reflector layer 440. A top surface of each QD layer 400 in thearray of QD layers may be level with a top surface of the Braggreflector layer 440 (e.g. they may have been planarized). A Braggreflector layer 465 and color filter layer 410 may be formed over thearray of QD layers 400 and the planarization layer 470.

A display system in accordance with embodiments may include a receiverto receive display data from outside of the display system. The receivermay be configured to receive data wirelessly, by a wire connection, byan optical interconnect, or any other connection. The receiver mayreceive display data from a processor via an interface controller. Inone embodiment, the processor may be a graphics processing unit (GPU), ageneral-purpose processor having a GPU located therein, and/or ageneral-purpose processor with graphics processing capabilities. Thedisplay data may be generated in real time by a processor executing oneor more instructions in a software program, or retrieved from a systemmemory. A display system may have any refresh rate, e.g., 50 Hz, 60 Hz,100 Hz, 120 Hz, 200 Hz, or 240 Hz.

Depending on its applications, a display system may include othercomponents. These other components include, but are not limited to,memory, a touch-screen controller, and a battery. In variousimplementations, the display system may be a television, tablet, phone,laptop, computer monitor, automotive heads-up display, automotivenavigation display, kiosk, digital camera, handheld game console, mediadisplay, ebook display, or large area signage display.

In utilizing the various aspects of the embodiments, it would becomeapparent to one skilled in the art that combinations or variations ofthe above embodiments are possible for forming a display panel andsystem with quantum dots integrated into the display area. Although theembodiments have been described in language specific to structuralfeatures and/or methodological acts, it is to be understood that theappended claims are not necessarily limited to the specific features oracts described. The specific features and acts disclosed are instead tobe understood as embodiments of the claims useful for illustration.

What is claimed is:
 1. A light emitting structure comprising: areflective bank structure; a light emitting diode (LED) mounted withinthe reflective bank structure; a passivation layer laterally surroundingthe LED within the reflective bank structure; a top electrode layerspanning over the LED, the passivation layer, and the reflective bankstructure; a film over the top electrode layer; and a cavity within thefilm, the cavity directly over the LED.
 2. The light emitting structureof claim 1, wherein the cavity is formed completely through a thicknessof the film.
 3. The light emitting structure of claim 2, wherein thereflective bank structure includes a reflective bank mirror that spansaround and underneath the LED.
 4. The light emitting structure of claim3, wherein the LED comprises an inorganic semiconductor-based p-n diode,and a metallic bottom contact.
 5. The light emitting structure of claim4, wherein the LED has a maximum width of less than 10 microns.
 6. Thelight emitting structure of claim 4, wherein the LED has a maximum widthof less than 5 microns.
 7. The light emitting structure of claim 3,wherein the LED comprises an inorganic semiconductor-based p-n diode,and a metallic bottom contact, and a reflective device mirror.
 8. Thelight emitting structure of claim 7, wherein the reflective devicemirror spans around and underneath the inorganic semiconductor-based p-ndiode.
 9. The light emitting structure of claim 8, wherein the LED has amaximum width of less than 10 microns.
 10. The light emitting structureof claim 8, wherein the LED has a maximum width of less than 5 microns.11. The light emitting structure of claim 2, further comprising: asecond reflective bank structure; a second LED mounted within the secondreflective bank structure; a second passivation layer laterallysurrounding the second LED within the second reflective bank structure;wherein the top electrode layer spans over the second LED, the secondpassivation layer, and the second reflective bank structure; and asecond cavity within the film, the second cavity directly over thesecond LED; wherein the LED and the second LED are designed fordifferent color emissions.
 12. The light emitting structure of claim 11,wherein the second cavity is formed completely through the thickness ofthe film.
 13. The light emitting structure of claim 12, wherein thesecond reflective bank structure includes a second reflective bankmirror that spans around and underneath the second LED.
 14. The lightemitting structure of claim 13, wherein the second LED comprises asecond inorganic semiconductor-based p-n diode, and a second metallicbottom contact.
 15. The light emitting structure of claim 14, whereinthe second LED has a maximum width of less than 10 microns.
 16. Thelight emitting structure of claim 14, wherein the second LED has amaximum width of less than 5 microns.
 17. The light emitting structureof claim 13, wherein the second LED comprises a second inorganicsemiconductor-based p-n diode, and a second metallic bottom contact, anda second reflective device mirror.
 18. The light emitting structure ofclaim 17, wherein the second reflective device mirror spans around andunderneath the second inorganic semiconductor-based p-n diode.
 19. Thelight emitting structure of claim 18, wherein the second LED has amaximum width of less than 10 microns.
 20. The light emitting structureof claim 18, wherein the second LED has a maximum width of less than 5microns.